A typical railroad car has an elongated frame and a pair of wheeled truck assemblies attached to the frame. Each truck assembly is attached to the frame at each end of the car. Each wheeled truck assembly in turn includes flanged wheels that are adapted to roll on a pair of railroad track rails.
With the wheels on the track rails, there may be clearance of only a few inches between the top of the railroad track rails and the underside of the railroad car frame. Routine maintenance may require that the car frame be elevated somewhat in order to increase this clearance. One form of maintenance may require that the railroad car be completely removed from one of the truck assemblies, to allow such truck assembly to be replaced with another. For example, to remove the assembly, the one end of the car may be lifted vertically about 10-25 inches, while the other end of the car remains supported on the other wheeled truck assembly. With the one car end so elevated, both the old and the new truck assemblies can be rolled along the rails. Other forms of maintenance may require a worker to crawl about beneath the car, and this increased clearance would also be beneficial.
One way of lifting one end of the railroad car is by means of a crane. This is done by connecting the lift line of the crane to the car frame, such as at the car coupling. This requires the presence of a high capacity crane that can carry the load of the car, and such a crane will typically be quite large and represent a significant capital investment. Moreover, such a crane may be mounted on a special railroad service car or road vehicle. If the crane limited to rolling along on track rails, it may not be conveniently moved from one site to another. If the crane is on a road vehicle, the crane may be used only at certain rail sites because of its size.
Another way the railroad car can be removed from the wheeled truck assembly is by means of a pair of separate lift jacks, interposed between the underlying rail bed and each side of the car frame. These jacks are relatively inexpensive, and quite portable. However, as the separate jacks bear against the rail bed, special shoring efforts may be needed in order to provide added stability to the jacks and to prevent the jacks from sinking into the rail bed. Moreover, with the jacks on opposite sides of the car, several people may be needed to operate the jacks.
Moreover, there are certain inherent risks with the use of either the crane or paired lift jacks because they bear the entire load of the railroad car during the time the wheeled truck is removed from the car or while someone is under the car for servicing. A crosswind may cause the crane-suspended car to sway, or the paired jack-supported car may topple sideways off of the jacks. This can be both dangerous to personnel and destructive to property. Dangerously, any failure of the crane lift line or of either jack can allow the raised car to fall.
U.S. Pat. No. 4,805,875 (“the '875 patent”) discloses a prior art railroad car jack assembly. This patent discloses a pair of rails and a multi-tiered cylindrical power lift system attached to a plate that engages and lifts the railroad car. The '875 patent also discloses a pair of side block bars that engage the railroad car engaging plate after the plate has raised the railroad car. The block bars provide added support to the car when the engaging plate is at the top of the operative range of movement. Both the power lift system and the block bars are actuated by a hydraulic fluid pumping system.
Although providing a substantial improvement over the prior art, the railroad car jack assembly in the '875 patent has some shortcomings, however. For example, the hydraulic pump system used is expensive, heavy and often requires significant maintenance. Also, the hydraulic lift system is raised and lowered in a somewhat long period of time.
Another prior art jack assembly, U.S. Pat. No. 1,745,959, provides a pair of telescoping posts to support the car engaging means so as to prevent the lifting means from buckling and tipping. While a pair of posts can prevent some angular rotation of the car engaging means, it generally acts to prevent such movement in a limited fashion.
The present invention is directed to an improved portable jack assembly that overcomes one or more of the drawbacks as set forth above.